1. Field of the Invention
The present invention relates to an apparatus for filling a cavity of a cell or laminated substrates with a fluid. The invention also relates to a method for filling the cavities of such cells or laminated plates with a fluid. After filling, if desired, a liquid may be converted into a solid. The method and apparatus are particularly suitable for making large area laminated glazings including electrochromic devices.
2. Description of the Prior Art
Laminated glass and cells that contain a liquid or a solid are well known. For example, some architectural and automotive laminate windows are fabricated from a pair of glass substrates and a solid film. The film is sandwiched between the two substrates and then subjected to a cycle of controlled heat and pressure (or vacuum) in an autoclave. This causes all the air to be expelled with a simultaneous softening and/or melting of the film that bonds to the substrates. When the cooled parts are removed from the autoclave an integral laminated unit is obtained. It is also known to seal the edges of the unit to protect the interior of the laminate from atmospheric elements. This method is well suited for self supporting films that can be handled in ambient atmosphere. However, if the materials for forming the interior of the laminate are sensitive to the ambient conditions or are tacky and not self supporting during handling then such a method may be impractical, particularly for commercial high-volume fabrication.
Various methods exist for filling the cavity of a cell or laminate with a liquid. For example, U.S. Pat. No. 5,151,816 discloses first preparing an empty cell using two substrates by sealing them at the periphery. A narrow interpane gap is obtained by adding a spacer to the adhesive used for the sealing operation or by employing a tape or a shim of a pre-determined thickness. Next, a liquid resin is introduced into the cell through a hole left in the seal or through a hole in one of the substrates. The air displaced due to the resin introduction is evacuated through another hole in the substrate or the seal by, for example, creating a suction with a syringe. However, this method is difficult to use if the liquid is being introduced to a large area cavity.
The use of air permeable but fluid impermeable seals through which the air is evacuated during the filling process is disclosed by U.S. Pat. No. 5,268,049. After the cavity is filled, all the holes are plugged and the liquid is converted into a solid. This method using air permeable seals, however, is not suitable for air sensitive materials.
The above-described methods of filling a cell cavity with a liquid, i.e., the two hole method or the method employing permeable seals, suffer from difficulties if the cavity to be filled is a large area. For example if the pressure on the liquid is increased to keep the filling process at a desired rate, the substrates or plates may bow and the force on the cell can lead to seal or plate failure. In addition, if a vacuum is applied to assist pulling the liquid through the cell, then the cell walls are likely to collapse inwards under the ambient pressure and thus restrict the flow of the liquid.
U.S. Pat. No. 5,142,407 discloses a method for filling a cell with a liquid using a technique described as vacuum backfilling. This method has been successfully used for filling smaller cavities in preparation of electrochromic devices. First, an empty cell having two substrates aligned with each other and separated by a seal having a small hole is fabricated. The cell along with the liquid to be filled is placed in a chamber. The chamber is evacuated and then the cell is lowered into the liquid so that the hole is immersed below the liquid meniscus. The vacuum is then released to a pressure p (e.g., atmospheric pressure).
The pressure P on the liquid forces it to fill the evacuated cell cavity. After filling, the cell hole is capped.
The success of vacuum backfilling depends on the pressure, the vacuum to which the cell was subjected to, vapor pressure of the liquid to be filled, the dimensions (thickness and size) of the cell cavity and the surface tension forces between the inner walls of the cell and the liquid. Using vacuum backfilling, the cell cannot be subjected to any arbitrary high vacuum, because the vacuum limit is determined by the vapor pressure of the liquid in the chamber. Thus, in order to successfully fill the cavity using this method, the use of low vapor pressure liquids are preferred. A relationship between the residual bubble size with the vapor pressure of the liquid and the cell size can be calculated. In addition, with increased cell size the size of chamber increases and the time for evacuation will increase both within the cell and in the chamber. For high surface tension liquids, pressure p will limit the extent of filling due to the gravitational forces. Therefore, vacuum backfilling is not a favorable process for filling large cell sizes such as typical automotive windows and architectural glazings.
It is also known that a liquid in the cavity of a cell may be solidified as disclosed in European Patent Application Publication No. 0612826A1. The typical solidification process is carried out by a thermally or radiatively induced polymerization process.
A method and apparatus for filling the cavities of larger area cells and laminates with a fluid that overcomes the above-mentioned difficulties would be highly desirable.